Hold a steel pole (or any solid, strong material) to your chest, start running as fast as you can and then drop that pole into the ground like a pole vaulter would. While laying on the ground sorting things out you can ask yourself if it was the pole that laid you out or if it was the solidity of the ground pushing back at you, the force, through the pole.

Assuming the pole is of sufficient diameter to not go through me when I drop it to the ground, what knocks me down is the fact that my chest and the end of the pole cannot occupy the same space at the same time. My forward momentum is stopped in the upper half of my body while the lower half of my body carries on, taking me off my feet. The kinetic energy I supplied by running experiences a sudden change of direction and I am, in effect, moving in two directions at once. The ground provides no force, only a stable place for the pole to rest.

Try the same experiment without any forward momentum supplied by you. Stand still and lean into the pole with all the energy you can muster... you will not fall... you will not be propelled backwards... you will not enjoy the feeling of the pole jabbing into your chest.